The present invention relates to a method performing a method for functional testing of a data collection system and at least one non-transitory computer-readable memory containing computer readable instructions for implementing this method. The method includes periodically sending by the message simulator to the data collection system running in production environment, batches of sets of messages, where the messages mimic normal client messages. Each message contains a batch identification common to the messages within the specific batch and a unique message counter value. The batch of messages received by the data collection system is checked in the verification service to verify whether the data collection systems operates correctly.